The present invention relates to an apparatus for exercising or rehabilitating neck extensors.
Most of the movements of the joints and especially limbs of the human body are based on a structure in which a tubular bone is joined to another tubular bone via a so-called hinge joint. The movement resembles the action of a mechanical hinge and takes place mainly two-dimensionally about a pivot point with a constant radius. An example of such movement is that of the elbow joint. However, the action of a hinge joint is not quite as simple as this, but this is the basic principle.
The action of the spine is not as simple as this. The spinal column consists of vertebrae and disks between them. Adjacent vertebrae are joined together via the disk and so-called facet joints. Successive vertebrae and the disk between them are called a functional spine unit (FSU). The movements of the spine cannot be described on the principle of the hinge joint, but the FSU always works in a three-dimensional fashion, comprising both rotation and sliding in different directions of motion.
Due to the structure of a pair of vertebrae, in which the facet joints and spinal processes limit the movement in the extension direction, the spine does not work like a hinge joint in the extension-flexion direction. The extension of the spine takes place as a series of xe2x80x9copening movementsxe2x80x9d of individual FSU structures as each inter-vertebral space is increased while the facets lean on each other. Correspondingly, the inter-vertebral space becomes narrower as the spine is flexed. This narrowing takes place as a series of flexion movements occurring progressively in motional segments from the top downwards. In movements in the flexion-extension direction, some sliding also takes place at the same time (Dvorak J and Dvorak V: Manual Medicine: Diagnostics. Georg Thieme Verlag, Stuttgart, 1990; Nordin M and Frankel V H (ed.): Basic Biomechanics of the Musculosceletal System: Lea Febiger, Philadelphia 1980; White A M and Panjabi M: The basic kinematics of the human spine 1978; 3:13 and White A M and Panjabi M: Clinical Biomechanics of the Spine. Lippincott, Philadelphia, 1978).
In consequence of this mechanism, the flexion movement of the spine does not follow a radial arc about a single centre, but the movement takes place on the principle of a changing centre of motion. For instance, by observing the path of the head, this results in a path resembling an elliptical rather than a circular arc. The radius of the ellipse is largest when the spine is fully extended and smallest when the spine is fully flexed.
In prior art, an apparatus for exercise and/or rehabilitation of neck extensors with flexion and extension movements between an extreme flexion position and an extreme extension position is known. The apparatus comprises an equipment frame, a seat provided with a back rest, and holding means for holding a person""s body substantially immobile in position in relation to the back rest. Furthermore, the apparatus comprises a link rod pivoted by its first end on the equipment frame via a first joint permitting a turning motion about a swing axis perpendicular to the vertical middle plane of the seat. In addition, the apparatus comprises a head rest functionally connected to the link rod so that the link rod participates in turning the head rest during an exercise movement while the person""s head is leaning against the head rest, and a resistance means for providing resistance to the exercise movement. An apparatus of this type is known e.g. from specification U.S. Pat. No. 5,336,138, wherein the head is held in a supporting frame acting as a head rest that holds the person""s head via contact with the back and sides of the head. The supporting frame is joined to the link rod. The lower end of the link rod is mounted with a ball joint on the back rest of the seat.
A problem with the prior-art apparatus is that the path of the part holding the head does not coincide with the natural path of motion of the head during flexion and extension of the neck because in the prior-art apparatus the turning motion takes place about a single centre, which means that the path is a circular arc. However, as stated above, the natural path of the head is not a circular arc but a path of a different type. In flexion and extension exercises with prior-art apparatus, an incorrect motional pattern is learned and the incorrectly applied load may result in a risk of injury. Besides, the chafing of the head against the head rest is annoying.
The object of the present invention is to eliminate the drawbacks described above. A specific object of the present invention is to disclose an apparatus in which a head rest path deviating from a circular path is achieved so that the head rest moves along a path corresponding to the natural path of motion of the cervical spine.
The apparatus of the invention comprises an equipment frame, a seat provided with a back rest, and holding means for holding a person""s body substantially immobile in position relative to the back rest; a link rod pivoted by its first end on the equipment frame via a first joint permitting a turning motion about a swing axis perpendicular to the vertical middle plane of the seat; a head rest functionally connected to the link rod so that the link rod participates in turning the head rest during an exercise movement while the person""s head is leaning against the head rest, and a resistance means for producing a force opposing the exercise movement.
According to the invention, the apparatus comprises adjusting elements for adjustment of the position of the seat in relation to the equipment frame. The head rest is substantially fitted to receive the upper part of the person""s neck, preferably the area of the topmost two cervical vertebrae. The apparatus comprises a multi-joint angular linkage mechanism, of which the link rod constitutes a part, said multi-joint angular linkage mechanism being connected to the head rest so as to cause it to move during an exercise movement along a curved path that substantially coincides with the natural path of the neck during flexion and extension movements of the neck without producing any relative motion between the head rest and the point of contact between the neck and the head rest.
Using the adjusting elements of the seat, a person can be individually positioned in a precisely defined position relative to the equipment frame and the mechanism turning the head rest. By fitting the head rest so that it meets the upper part of the neck, preferably the area of soft tissue of the neck, which lies in the upper region of the cervical spine in the area of the topmost cervical vertebrae c1 and c2, an exercise movement is achieved that does not stress the muscles connecting the cranial base to the upper part of the cervical spine, thus ensuring that no sliding occurs between the topmost cervical vertebrae as in prior-art apparatus. The multi-joint angular linkage mechanism allows head rest motion along a path corresponding to the natural path of neck motion so that the head rest does not move in relation to the neck during exercise and no mutual chaffing occurs but the head rest follows the same path with the neck. The magnitude and application of stress following natural paths can be adjusted during physical exercise. The advantages of stress following natural paths include the following. During exercise, the stress is applied in the correct manner to the tissues to which it is intended to be applied. Furthermore, correct motional patterns are learned. This means that the motional patterns learned during exercise are likely to be correctly observed even outside the exercise or rehabilitation situation. In addition, the risk of injury due to incorrect stress during exercise and rehabilitation is reduced.
In an embodiment of the apparatus, the path of the head rest is a path with a varying radius, such as an elliptical path. As the flexion-extension movement of the spine does not take place along a radial arc about a single centre but occurs on the principle of changing centre of motion, the head rest preferably follows a path resembling an elliptical curvature. The radius of the ellipse is at a maximum when the spine is completely extended and at a minimum when the neck is completely flexed.
In an embodiment of the apparatus, the multi-joint angular linkage mechanism is functionally a so-called five-joint planar mechanism. The apparatus comprises a control gear for controlling the motion of the multi-joint angular linkage mechanism. The control gear is rotatable about a swing axis immovable with respect to the equipment frame. The swing axis is disposed at a distance from the first joint but in its vicinity. It is obvious that suitable paths can also be achieved using other types of planar multi-joint angular linkage mechanisms.
In an embodiment of the apparatus, the apparatus comprises an auxiliary link rod whose first end is pivoted on the equipment frame via a second joint disposed at a distance from the first joint but in its vicinity. The apparatus further comprises a head rest support to which the head rest is attached, the second end of the auxiliary link rod being pivoted on the head rest support via a third joint. The control gear comprises a first frame component, which is rotatably mounted on the equipment frame and provided with a first guide disposed at a distance from the centre of rotation of the first frame component, and a second frame component, which is provided with a second guide, forming a guide pair with the first guide, permitting movement of the second frame component in a direction determined by the guides in relation to the first frame component. The head rest support is pivoted on the second frame component via a fourth joint, which is at a distance from the third joint. The second end of the link rod is pivoted on the second frame component via a fifth joint, which is at a distance from the third joint and the fourth joint. Thus, the five-joint planar mechanism consists of the rigid parts of the mechanism and equipment frame between the first, second, third, fourth and fifth joints.
In an embodiment of the apparatus, the link rod comprises second adjusting elements to allow adjustment of the distance between the first joint and the fifth joint, i.e. of the length of the link rod between the joints. Further, the auxiliary link rod may comprise third adjusting elements to allow adjustment of the distance between the second joint and the third joint, i.e. of the length of the link rod between these joints. By adjusting the lengths of these link rods of the multi-joint angular linkage mechanism, the path of the head rest can be adjusted individually for each person.
In an embodiment of the apparatus, the apparatus comprises a resistance means to provide resistance to the turning motion of the link rod and/or auxiliary link rod.
In an embodiment of the apparatus, the apparatus comprises a turning arbor rotatably mounted with bearings on the equipment frame. The first frame component is attached to the turning arbor. The resistance means is connected to the turning arbor to generate a torque opposing the rotation of the turning arbor.
In an embodiment of the apparatus, the resistance means works on a gravity resistance principle. The resistance means comprises a counterweight consisting of a number of individual weight elements of a given weight, which can be combined so as to create a predetermined load.
The resistance means comprises an eccentric gear connected to the turning arbor and comprising an eccentric surface or the like. A flexible elongated draw element is connected to the counterweight and, on the other hand, arranged in functional contact with the eccentric surface or the like. As the draw element is wound around the eccentric surface or the like, a load opposing the exercise movement with a force that varies in a predetermined manner as a function of the rotational angle of the turning arbor.
In an embodiment of the apparatus, the first frame component comprises a balancing counterweight for balancing the structural assembly rotating about the swing axis. Thus, the apparatus permits a so-called zero stress situation to be achieved, which means that it does not generate any resistance to the turning movement of the head rest.
In an embodiment of the apparatus, the first frame component comprises fourth adjusting elements for the adjustment of the distance of the balancing counterweight from the swing axis.